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-   -   wall functions (http://www.cfd-online.com/Forums/fluent/70104-wall-functions.html)

thecfduser November 14, 2009 13:26

wall functions
 
Hello everybody
i have a question about wall functions in Fluent:
1- Is wall function applied only for the first near wall cell, or for the whole boundary layer???
2- To calculate the velociy values using wall functions, we need to have the friction velocities. Anyone can tell me how Fluent calculate the friction velocity?
Thanks

bob12 November 14, 2009 15:28

i think that you know becouse don't see the velocity profile near a wall with your simulation. this depend on the mesh that aren't sufficiently accurete, so i'm sorry but you take gambit and near the wall you reduce a size of mesh.
i understend your question?
i hope useful
bye
p.s. for how cumpute the value, fluent use the differential equations and trasform it in algebric equation approsimate that function with a difference (as such as the definition of derivative in mathematics) and the residual is the error that fluent introduced in this operation.

arslan November 15, 2009 16:16

1. B.C. only for the first cell, in the boundary layer Fluent calculate according to 'wall functions'
about second question i not understand what u want to compute and what you meen by "friction velocity"

thecfduser November 16, 2009 05:42

Thank u comrade
u responded to my second question too :)
friction velocity is uf (u+=u/uf)
regards


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